Abstract The United States occupies absolute power superiority in the AsiaPacific security order, the ASEAN plays a central role in the regional mechanisms and norms, and China plays a leading role in promoting regional conceptual consensus. Various agents with its own advantage are not only the source of the weak stability of the Asia-Pacific security order, but also main factors of affecting the maintenance of regional order and structural change. The security cooperation between the United States, the United Kingdom and Australia can be traced back to the military cooperation during the Second World War, and the trilateral cooperation has challenged the regional and international order from the dimensions of power, concepts and institutions. Since September 2021, the trilateral security partnership between the US, the UK and Australia is bringing many challenges to the Asia-Pacific security order. The security partnership will complicate the power structure in the AsiaPacific region and weaken the regional and international arms control system in terms of the power dimension. The emphasis of minilateralism identified by the three sides at the conceptual level will strengthen the regional camp confrontation and divergence. While weakening the influence of the ASEAN-led mechanisms and norms, the implementation of tactics of securitization will increase the instability of the AsiaPacific security order.